Microstructural and in vitro characterisation of High-Velocity Suspension Flame Sprayed (HVSFS) bioactive glass coating

The paper reports the first attempt at employing the innovative High-Velocity Suspension Flame Spraying (HVSFS) technique in order to deposit bioactive glass coatings. Fine (micrometric) glass particles having a composition similar to that of the A-W (apatite-wollastonite) bioactive glass-ceramic as proposed by Kokubo were dispersed into a 50% water + 50% isopropanol solvent mixture and the resulting suspension (containing 20 wt.% glass powder) was thermally sprayed onto Ti plates using a modified high velocity oxy-fuel torch.Each torch pass produces a dense coating layer, featuring strong cohesion between lamellae thanks to viscous flow sintering along the interlamellar boundary. However, some porosity exists between different layers deposited during successive torch passes.In-vitro bioactivity tests indicate that the coatings interact remarkably with the simulated body fluid (SBF), developing a thick silica-rich layer containing hydroxyapatite crystals.